In a Code Division Multiplex Access (CDMA) communication system, an air interface refers to a transmission link between a base station and a terminal; and the size of capacity of the air interface mainly depends on forward/backward link interference, Channel Element (CE) resources, power resources and other factors. In the air interface link data transmission, a forward traffic frame transmitted by the base station comprises a full rate frame, a ½ rate frame, a ¼ rate frame and a ⅛ rate frame. The ⅛ rate frame is used for carrying background noise and may not transmit actual speech contents, while other rate frames all carry speech contents. The ⅛ rate frame occupies a very large proportion and is often over 60% in a communication process, so that the transmission of many ⅛ rate frames may increase forward interference and cause the waste of air interface resources.